1. Field of the Invention
The present invention relates to an adhesive composition and to an adhesive sheet suitable for use in semiconductor devices using various semiconductors, particularly a semiconductor device having a structure in which an IC chip is laminated on an IC board consisting of an IC insulator layer and a conductor circuit, a surface-mounting type semiconductor device and a multi IC chip type semiconductor device, and more particularly relates to an adhesive composition and an adhesive sheet for bonding an IC chip or a radiator plate, or laminating with an increased density on an IC board, i.e., for bonding an IC chip to an IC board, insulating layers together for a higher-density lamination on an IC board, an IC chip and a radiator plate, a radiator plate and an IC board, and/or IC chips together.
2. Description of the Related Art
With the recent spread of portable personal computers and cellular phones, there has been an increase in demand for electronic equipment which is reduced in size, is thicker, and is multifunctional.
In order to meet these demands, electronic parts must be reduced in size with an increased scale of integration, and furthermore, a high-density mounting technique of electronic parts is necessary.
As for IC packages constituting the core of electronic parts in recent years, periphery-mounting types such as a QFP (Quad Flat Package) and an SOP (Small Outline Package) have been typically used. Recently, however, IC packages of a surface-mounting type called BGA (Ball Grid Array), CSP (Chip Size Package) and BOC (Board On Chip) and packages of a multi IC chip type called MCP (Multi Chip Package) have been highlighted as IC packages capable of high-density mounting.
In the BGA, CSP and BOC, solder balls are provided in the form of a surface lattice on their back surface as connecting terminals to the outside. An electrode of the IC (semiconductor integrated circuit) is connected to an electrode of a printed circuit board through an IC board or wiring-pattern-of-a-circuit switching board. There have been developed, depending on the type of the IC board, a plastic BGA (hereinafter referred to as xe2x80x9cP-BGAxe2x80x9d), a ceramic BGA (hereinafter referred to as xe2x80x9cC-BGAxe2x80x9d), a tape BGA (hereinafter referred to as xe2x80x9cT-BGAxe2x80x9d), an enhanced BGA (hereinafter referred to as xe2x80x9cE-BGAxe2x80x9d) and the like.
Until recently, the P-BGA, which is capable of making use of a wire bonding technique in the QFP, has been widely used. However, the T-BGA which utilizes a TAB (Tape Automated Bonding) technique is becoming increasingly common because it enables further densification (pin multiplication) and is excellent in heat radiation.
The CSP is a package made by further size reduction and densifying the BGA and is called a xe2x80x9cmicro-BGAxe2x80x9d or xe2x80x9cfine pitch BGAxe2x80x9d. Owing to its structure, the CSP has excellent electrical reliability such as low impedance and a rapid frequency response.
One example of a fine pitch BGA is shown in cross section in FIG. 1.
An IC board 1 in this example consists of an insulator layer 2 and a conductor circuit of a conductor electrode 3 and the like formed on one surface of the insulator layer 2, with a central hole provided therein. The IC board 1 is laminated through an adhesive layer 4 on an IC chip 5. The IC chip 5 is connected through a bump formed thereon to the conductor electrode 3 with a metal wire 6. The wiring and connections are covered with resin 7. Wiring 8 is formed on those portions of the conductor electrode 3 that are not covered with resin 7, with a solder ball 9 formed on the wiring so as to electrically connect the BGA to the outside.
Another example of a fine pitch BGA is shown in cross section in FIG. 2. An IC board 1 in this example consists of an insulator layer 2 and a conductor electrode 3 formed on one surface of the insulator layer. The insulator layer 2 is provided with a plurality of throughholes for solder connection, from the side where the conductor electrode 3 is not formed, to the conductor electrode. A first IC chip 5a and a reinforcing plate 10 are laminated through an adhesive layer 4 onto the conductor electrode 3 formed on the insulator layer 2, and a second IC chip 5b is laminated through an adhesive layer 4 on the first IC chip 5a. The IC chips 5a and 5b are connected through bumps formed thereon to the conductor electrode 3 with metal wires 6. The wiring and connections are covered with resin 7. A solder ball 9 is formed in the throughholes provided in the insulator layer 2 so as to come into contact with the conductor electrode 3 and electrically connect the BGA to the outside.
Another example of a fine pitch BGA is shown in cross section in FIG. 3. In the fine pitch BGA of this example, a conductor electrode 3 and an IC chip 5 are laminated through an adhesive layer 4 on one surface of a radiator plate 11. On that surface of the conductor electrode 3 which has no adhesive layer 4 thereon, an insulator layer 2 is provided which has throughholes for solder connection to the conductor electrode 3, so as to constitute an IC board 1. The IC chip 5 is connected through a bump formed thereon to the conductor electrode 3 with a metal wire 6. The wiring and connections are covered with resin 7. A solder ball 9 is formed in the throughholes provided in the insulator layer 2 so as to come into contact with the conductor electrode 3 and electrically connect the BGA to the outside.
For forming the insulator layer 2, which constitutes the IC board, a board material employing polyimide resin, epoxy resin, phenolic resin or the like is usually used. Furthermore, for forming the adhesive layer 4, an epoxy resin/NBR (acrylonitrile-butadiene copolymer) based adhesive, an epoxy resin/phenolic resin based adhesive and a rubber-modified epoxy resin/phenolic resin based adhesive have conventionally been used.
An IC package, when driven, reaches temperatures of 100xc2x0 C. or more due to heat generated by the IC and is exposed to changes in temperature from room temperature to an elevated temperature (100xc2x0 C. or more). Accordingly, the IC package is required to have heat resistance to withstand the stress changes in that case, humidity resistance under high temperature conditions, and a stress relaxing property.
Especially in recent years, the mounting density has been increased, with the result that the proportion of wired conductive metal is made larger, thereby making it necessary to bond together materials having different coefficients of thermal expansion. An IC package is also required to be capable of withstanding stresses caused in that case. The adhesive as composed above, however, does not have sufficient resistance to long-term temperature changes, nor sufficient resistance to high temperatures and high humidity.
More specifically, due to the stress resulting from repetition of cycling the temperature change between room temperature and an elevated temperature (100xc2x0 C. or more), delamination often occurs between the above IC-board-constituting insulator layer 2 and the IC chip 5, or inside the laminated board. Furthermore, as a method for enhancing the mounting density, insulator layers may be laminated to form a three-dimensional wiring pattern. This method also has the same drawback. In this laminating-type high density mounting method, as laminating substrates, there has been in many cases employed, in addition to a glass epoxy board, a TAB board, a flexible board or the like for the purpose of thinning the package, most of the materials of which are polyimide resin and the like.
Generally speaking, polyimide resin and the like are very difficult to bond and are susceptible to influences from the conditions of absorbed water, interface and the like. Thus, an adhesive composition of low water absorption and excellent adhesion has been demanded.
Furthermore, in this laminating-type high density mounting method, a wiring pattern must be embedded during lamination. Thus, an adhesive composition has been demanded which is free of resin flow during the embedding and free of foaming during bonding.
Furthermore, with elevation of an IR reflow temperature due to the lead-free tendency in recent years, the water contained in an adhesive is likely to vaporize and push aside the adhesive during the reflow, thereby giving rise to a blister-causing water-vapor explosion called a popcorning. Therefore, in order to remove the popcorning-causing water content, semifinished products prior to the reflow have been managed under moisture excluding conditions. However, since management under moisture excluding conditions requires much labor and cost, an adhesive composition has been demanded which does not give rise to the popcorning if not managed under moisture excluding conditions.
Furthermore, in view of its application to a conductor portion, an adhesive composition is required to have electrical reliability.
The present invention has been made to overcome the above drawbacks, and one of its objects is to provide an adhesive composition and an adhesive sheet for semiconductor devices, which overcome the drawback in the conventional adhesive compositions used in semiconductor devices such as BGA and CSP or the drawback of delamination caused by temperature cycling; in other words, which are excellent in stress relaxation and heat/thermal cycle test.
Another object of the present invention is to provide an adhesive composition and an adhesive sheet for semiconductor devices in which adhesive resin does not flow and there is no foaming during bonding and curing, which occurred in the conventional adhesive compositions.
A further object of the present invention is to provide an adhesive composition and an adhesive sheet for semiconductor devices that are excellent in electrical reliability and strength of adhesion to copper, polyimide and the like.
Yet another object of the present invention is to provide an adhesive composition and an adhesive sheet for semiconductor devices which overcome the drawback in the conventional adhesive compositions or the popcorning caused by vaporization of the water contained in the adhesive composition during the reflowing; in other words, which have excellent resistance to humidity.
In order to attain the objects, according to one aspect of the present invention, there is provided an adhesive composition for semiconductor devices, which comprises (A) epoxy resin, (B) phenolic resin, (C) epoxidized styrene-butadiene-styrene block copolymer, and (D) diaminosiloxane compound.
Preferably, a ratio of the (A) epoxy resin to the (B) phenolic resin is 1:0.6 to 1:1.4 in terms of an equivalent ratio of functional groups.
Preferably, a ratio of the (C) epoxidized styrene-butadiene-styrene block copolymer is 30 to 80% by weight of a total solid content of the adhesive composition.
Preferably, a weight ratio of butadiene to styrene in the (C) epoxidized styrene-butadiene-styrene block copolymer is 1/99 to 70/30.
Preferably, an epoxy equivalent of the (C) epoxidized styrene-butadiene-styrene block copolymer is 140 to 6000.
Preferably, the (D) diaminosiloxane compound is a diaminosiloxane compound having an amino group at both ends represented by a general formula (1): 
wherein Rxe2x80x2 is an alkylene group having 1 to 10 carbon atoms and n is an integer of 0 to 10.
Preferably, the (D) diaminosiloxane compound is 0.3 to 10% by weight of a total solid content of the adhesive composition.
According to another aspect of the present invention, there is provided an adhesive sheet for semiconductor devices, which comprises a support and an adhesive composition as mentioned above, laminated on at least one surface of the support.
Preferably, the support comprises an insulating film or releasable film.